Rough idle and dies when I put it into driver or reverse
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
I just ordered AC delco O2's. I should have them in on Monday. I havenot tried to unplug the O2 yet. What should happen?
The Opti was from ebay. Some off brand rebuild. If I knew that the Opti's were problematic when I bought it, I would have bought a GM brand opti. I'll get back to the forum on Monday after installing the O2's.
I'll also check the cam sensor. The car runs great when I drive it. It is just idle RPMS. Would a cam sensor only effect idle?
The Opti was from ebay. Some off brand rebuild. If I knew that the Opti's were problematic when I bought it, I would have bought a GM brand opti. I'll get back to the forum on Monday after installing the O2's.
I'll also check the cam sensor. The car runs great when I drive it. It is just idle RPMS. Would a cam sensor only effect idle?
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
Checked wires. Drivers side is easy. Passenger is a more challenging. All are in the correct places. I hope the O2's are the problem cause the Opti look like a whole day job.
Cam position Sensor's are real enough, as are crank position sensor..... when the CPS when out in the Mercury, it burned up with the coils, it did somthing similar although it wouldn't stay started for in park for longer then 3 seconds.... Although im not sure how the LT's are set up, if you replaces your opti, maybe coulda replaced a CPS too. This is speculation though cause again, Ive never actually worked on an LT motor....
I had the same issues as you.. It's the cam sensor, behind the intake.. It's hard to get to. You'll have to take the intake off to put a new one on. You can unplug it if you reach back there, just can't swap it out.. If your car isn't acting up, you can try unplugging it, starting the car up and cycling the keys a couple of times to see if it is producing the symptoms that you have been experiencing.. I wouldn't drive it that way or rev or anything like that though.
I've heard a crank sensor will give you similar symptoms, but haven't had any problems with mine yet.
I've heard a crank sensor will give you similar symptoms, but haven't had any problems with mine yet.
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
So i replaced the O2's with AC delco and theproblem is still there. I'm still baffeled on where the can sensor is. i am getting a code 97 vss circuit error. My MPH are registering. Would that effect my idle?
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you said that the car has Heads and a cam.....this could possibly just be in the idle section of the tune. You also said when you unplug your MAF the car doesn't get any different or worse...this indicates that the tune could be off. Who did the tune in the car?
Also when my car went into limp mode from launching to fast on the stock trans tune with a big converter I also got that VSS code but there was nothing actually wrong except for that the computer went into limp mode. This was caused by high engine rpm and a low vss reading making the computer think that the trans was bad/slipping.
Also when my car went into limp mode from launching to fast on the stock trans tune with a big converter I also got that VSS code but there was nothing actually wrong except for that the computer went into limp mode. This was caused by high engine rpm and a low vss reading making the computer think that the trans was bad/slipping.
http://www.carcraft.com/howto/ls1_en.../photo_09.html
EDIT: Another page to help with location/look..
http://chevythunder.com/ls1_page_1.htm
Last edited by Slvr00Bird; Nov 3, 2009 at 02:11 PM.
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
Update and recap of diagnostics 11/3/09
• New plugs and wires – not burnt or fouled. Wires are in correct order.
• New opti
• New TPS
• Cleaned MAF filament. Unplugging MAF does not change the way the car idles
• No vacuum leaks. Searched by spraying engine start around the engine
I have a solid fuel pressure. I checked while driving and it stayed between 40 and 47 PSI. Double checked Fuel pressure and found 46 PSI at idle and 50 with the vacuum unplugged. Fuel system holds pressure.
• New fuel filter
• No arc’s in wires – checked at night
• Bored out 52mm TB – bought from eBay remanufactured
• No EGR. I have a block off plate
• No Cats
• Rewired and checked park neutral switch
• Checked electrical ground straps
• Changed O2’s to AC Delco
• Lt1pcmtuning base tune – fine tuning coming this week
• Can’t find Cam sensor. I’m pretty sure I do not have one or it might be built into the distributor
Suggestions anyone?
• New plugs and wires – not burnt or fouled. Wires are in correct order.
• New opti
• New TPS
• Cleaned MAF filament. Unplugging MAF does not change the way the car idles
• No vacuum leaks. Searched by spraying engine start around the engine
I have a solid fuel pressure. I checked while driving and it stayed between 40 and 47 PSI. Double checked Fuel pressure and found 46 PSI at idle and 50 with the vacuum unplugged. Fuel system holds pressure.
• New fuel filter
• No arc’s in wires – checked at night
• Bored out 52mm TB – bought from eBay remanufactured
• No EGR. I have a block off plate
• No Cats
• Rewired and checked park neutral switch
• Checked electrical ground straps
• Changed O2’s to AC Delco
• Lt1pcmtuning base tune – fine tuning coming this week
• Can’t find Cam sensor. I’m pretty sure I do not have one or it might be built into the distributor
Suggestions anyone?
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
This should give you an idea of what it looks like and where it is.. The cam position sensor is located at the rear of the block, behind the intake manifold, and above the camshaft.
http://www.carcraft.com/howto/ls1_en.../photo_09.html
EDIT: Another page to help with location/look..
http://chevythunder.com/ls1_page_1.htm
http://www.carcraft.com/howto/ls1_en.../photo_09.html
EDIT: Another page to help with location/look..
http://chevythunder.com/ls1_page_1.htm
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
One thing that came to mind was that I never readjusted the valves after I got the engine running. The Engine was rebuild with all new parts. Could the initial valve adjustment be off causing idle issues? I'm going to do that tomorrow.
Unless its a solid roller I doubt it and even then I still doubt it. If you hear any clicking like excessive lash fix it, but this still won't cause this. Again, I am leaning towards the tune itself.
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
Next is a fine tune of the PCM base tune and a engine off but hot valve adjustment. I'll post back tommorrow. I have a job interview today and I don't want to get the hands dirty.
Overlooked that piece of information.. Could be the crank sensor then.. I've heard it has similar symptoms.. It'd probably be easier to check the tune though.. and then if not, go from there.. If it always does it, then I'd say it's in the tune.. If not, sensor..
I wouldn't waste my time with the valves though..
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
On an LT1, the cam and crank sensor functions are part of the optispark. On OBD-II LT1 cars, there is a separate crank position sensor in the timing cover, but it has nothing to do with spark delivery and is only used to compare signals to the crank info from the opti to determine misfires. The engine can even run without that crank sensor.
An off brand Ebay opti is a good suspect for problems.
An off brand Ebay opti is a good suspect for problems.
Thread Starter
Staging Lane
Joined: May 2008
Posts: 75
Likes: 0
From: San Francisco, CA
OK guys. I think i found the major problem here. I replaced the IAC and it does not stall when putting into gear anymore. YAY!!! The car does stumble a bit when going into gear but not enough for it to die. My old IAC was working but I think it was acting a little sluggish and not reacting to fluctuating idle RPM fast enough. The new one does a better job at keeping an idle but I do notice it working. Thanks for all your help everyone.